pytz has so many timezones!

[J. Clifford Dyer]

On Mon, Oct 08, 2007 at 10:41:03AM -0700, mensanator at aol.com wrote regarding Re: pytz has so many timezones!:
> 
> On Oct 8, 2:32 am, Sanjay <skpate... at gmail.com> wrote:
> > Hi All,
> >
> > I am using pytz.common_timezones to populate the timezone combo box of
> > some user registration form. But as it has so many timezones (around
> > 400),
> 
> There are only 25 timezones: -12, -11, ... -1, 0 (GMT), +1, ... +11,
> +12.
> 
> A handful of countries set their clocks offset by a half hour,
> but those aren't timezones.
> 

I'm sorry.  By what even vaguely useful definition of "Timezone" is it not a timezone if it's offset by half an hour?  

> 
> The 400 you're seeing are duplications based on locality. Of the 86
> shown in Windows, all but 33 are dulplicate references to the same
> timezones.
> 
> For example, Windows has seperate listings for
> 
> Central America
> Central Time (US & Canada)
> Guadalahara, Mexico City, Monterry - New
> Guadalahara, Mexico City, Monterry - Old
> Saskatchewan
> 
> but they are all GMT-6
> 

Those are non-duplicate (and perhaps inaccurate, I'm not sure).  US time switches from standard to Daylight Savings earlier than Mexico, and switches back later, as of this year.  Reducing them to a single time zone will result in aberrant functionality in one or more locales.

Cheers,
Cliff